Detection of the state of a human living body, for instance, whether it is in an activation state (awakening state) or in a sleeping state is conventionally carried out by measuring a brain wave, and analyzing its brain wave pattern. However, measurement of a brain wave is required to perform in an environment to restrict usual behavior of a person such as attachment of brain wave electrodes or eye potentiometric electrodes on a head of a testee. Therefore, it is difficult to evaluate, for instance, the state of a living body during driving various transportation machines such as cars or trains without imposing a burden on a driver.
Whereas, monitoring the state of driver's living body (state of mind and body) during driving has been widely noticed as a safeguard against traffic accidents in recent years. For instance, in Patent Document 1 (Japanese Patent Application Laid-open No. Hei 9-308614) and Patent Document 2 (Japanese Patent Application Laid-open No. Hei 10-146321), a technology of monitoring the living body state using a heart beat or blood beat has been proposed. According to the technology disclosed in Patent Documents 1 and 2, it is possible to easily evaluate a living body state of a driver without installment of a large scale device for brain wave measurement on a head.
All of the devices disclosed in Patent Documents 1 and 2 calculate a chaos index of heart beats or blood beats, from which the state of mind and body of a driver is judged. Concretely, it is structured as follows. As one of the chaos indexes, Lyapunov index of heart beats or blood beats is determined, and when decrease in the Lyapunov index is seen during a prescribed period of time or longer in the time base change, it is determined that a stress load is generated in a level requiring a rest and a testee is in a state just before falling into a doze (the state of feeling drowsy). It has been already reported by Japanese Patent Application Laid-open No. Hei 4-208136 that a living body state could be objectively determined by the chaos index as a signal for a living body, and it may be possible to detect a state immediately before falling into a doze by a device disclosed in Patent Documents 1 and 2.
However, Patent Documents 1 and 2 only disclose that the technology treats measured heart beats or blood beats with only a chaos index such as Lyapunov index or the like, and detects a process from a change in decrease in Lyapunov index to a mentally stable state, and determines whether or not a fatigue state in such a degree of drowsiness is generated, but no trial has been made to grasp the degree of fatigue quantitatively.
Generally, as for a body force, there are vital body force relating to maintain a life, and an active body force with a background of the viable body force. The viable body force corresponds to a capability to maintain life and health, and is also called a defensive body force, while the active body force is a behavioral body force to move a body, and is generally taken as motility. The functions to support the behavioral body force include an energy generating system, an energy supplying system, and an energy control system. The energy generating system relates to a function to cause muscle fatigue of muscular strength, endurance, or the like, depending on the manner of muscular system workings. The energy supply system relates to a function of respiratory and circulatory system determined by oxygen intake or heart rate, and the energy control system relates to a function of agility, cooperativity, balancing ability, and flexibility. Therefore, as a consequence, physical burden can be determined from the state of the energy supply system, and mental burden from the state of the energy control system. From these judgment, an active state of the energy generation system which is a basis of muscle fatigue can be grasped.
The state of the above-described energy control system, namely, the conditions of mental burden can be grasped by determining Lyapunov index of living body signal data, and the state of the above-described energy supply system, namely, the state of physical burden can be grasped by measuring and treating force of resistance (referred to as “a power value” in the present specification) determined from a peak value in a cycle of the living body signal. In other words, an ACTH emission hormone is allowed to create various biological activities by a living body reaction called a general adaptation syndrome produced when various stressors are added to a living body. The force of resistance is a power which fights invasion and destruction from outside and includes such reactions as autonomic nervous system reactions shown by increase of heart rate caused by the reaction or increase in offensiveness, and results in consumption of energy and emission of calories. Accordingly, it is effective to determine the fatigue degree by detecting a decline in consumed calorie. In the present invention, such a force of resistance is determined from the peak value in a cycle of a living body signal, which is defined as a power value.
As for fatigue, there are peripheral fatigue and central fatigue. For instance, in the state of seated on a car seat for a long time, though there is an individual difference due to conditions of the seat or physical conditions, generally, the peripheral fatigue is predominant in the first half and the central fatigue is predominant in the latter half. As for the process of fatigue, a testee may begin to relax while calorie consumption is kept high and then calorie consumption declines, or calorie consumption may decline while a testee is excited, and then the testee relaxes to further lower calorie consumption. That is, a decline in consumed calorie commonly occurs in both fatigue, and it is conceived to be effective for grasping fatigue to analyze a power value from this point of view. However, conventionally, analysis of Lyapunov index is exclusively used to detect fatigue in the state of just before the onset of sleep from a mental burden, and since analysis of a power value is not taken into consideration, it is not suitable especially for detection of peripheral fatigue.
Furthermore, the values of Lyapunov index and heart beat in Patent Document 1 and 2 are taken in a time series change, but they are values for every 15 minutes or 30 minutes. Therefore, substantially real time state change necessary for monitoring during driving cannot be observed.
The present invention is achieved in consideration of the above-described problems, and an object of this invention is to provide a fatigue degree measurement device which can realize quantification of the degree of fatigue, can detect a fatigue signal irrespective of peripheral fatigue or central fatigue, and is suitable for measuring the degree of fatigue and detecting fatigue of, in particular, a driver, a fatigue detecting means, and computer programs.